Method of forming a wet cathode portion



June 23, 1953 H. M. ZIMMERMAN METHOD OF FORMING A WET CATI-IODE PORTION Filed Dec. 22, 1948 l il Il Il Il il u QN INVENTOR HERMANv M. ZIMMERMAN Patented June 23,

M non F Fotgm e 2* Y Po TION y Aiiili ljceinber 22, 194s, serialNo. 66,785

the *meer` 1mm-fry es slfevinge mensuelle made steh txaeke efefifmfrywhen ary and tend .to eek@ up wiel the blagcg spread e lye; te@ 't rter ni wie@ mj` (c1. laam) Y Y op He anitaeseinbly; the height of the ring' -being eh'thtt 'the oben-Gente? portion of vtherng;

time' within th old en fiom the tap blade I3 is preferably enough to rest on opposite sides of the ring. The

surface is at a slight angle to: the horizontal in order to obtain a better smoothing andvpreliminary compressing action on the carbon particles I2 or, if desired,-the surface, of the blade which cooperates with the carbon particles may be given this upward inclination.

The wet portion of the cathode contains, typically, 200 parts by weight of acetylene black and 519 parts 'by weight of aqueous 10% zinc chloride solution-and has l5-20% ofl itsvolume as open pores.A 'Variations in` the materials, famounts thereof and porosity` `or percentpores may be in accordance Vwith vthe description inthe prior applicationof ,Heise and Schumacher, Serial No.4

52,472, filed October 2, 1948, for fPrimary Cell and'Batteryand Method of Making Same now PatentlNo. 2,612,532, dated September 30, 1952, and the prior applicationofCahoon andv Heise, Serial'No..52,988,.lted October 6, 1948, for Pritilted So VthatV its 'Bettoni f Vshown in Fig. 2, the bladepreferably being long Y maryjGalvanic Cell andBattery and Method of Y Making Same, now Patent No. 2,612,538, dated' September 30, 1952. In, this. moist mix the mois; ture Vconstitutes a binder for the carbon particles, as well as laterk serving asielectrolyte shrte'n'the time required for this wetting operatio'n and to facilitate the .penetration of the moisture into the mix, the electrolyte solution ofY 10% zinc chloride preferably has added thereto about 1% of some stable'wetting agent, Vsuch as awater.

solution of "sodium Z-ethylhexyl sulphate' l' '(Clrnonirczni ccnzsolria) or other stable wetting agent` such as Will occur to those skilled in the (art. lAlcohol or acetone in similar concentrations` are also effective.

nIn the lpreferred practice, on top of the mold solvent. To

II and contacting the smoothed oicarbon Wasfa Munising #2-1089, about .004 in thickness, the same being an alpha-cellulose Vbase impregnated with a melamine resin to hold the fibers together when wet. Thin kraft paper is equally suitable. This paper easily transmits water but carbon particles do notadhere toit as they do to a' Vfuzzier and softer material, for instance, blotting paper, presenting unbound and uncoated fibers. LOver the paper I4 is laid a wet'bibulous material I5, such as blotting paper soaked in water or electrolyte solution, to whichv the wetting agent is added,V if desired. The particular blotting paper used was Economy White or Wrenns Bluebird 140 lb. blotting paper cut into sheets. Upon the application'oi pressure to the wet blotting paper either by'a rolling platen or a plunger type of pressure applicator I6, moisture is pressed from the bibulousmaterial I5 through the paper I4' into the mix I2, which after receiving its moisture is designated by the numeral I2. Too much moisture inthe ,mixris' not desirable' for a cell illustrates the effect of mix wetness within the preferred range on cell performance:

,Mix wetness Discharge Voltage at 1.42 Watts/Sq. In.

itrazm'f n 2 solultion per v Mmlttes; Qn Tes? Aver- 0.4 gram of age 1stdry black 0 l 2 3 '4 5 8 5 Mm.

1. 8S 11584 83 1. 82 1. 81 1. 80 1. 78 1. 83 1:90'v '1. 80 YA1183 1.85 1.85 1.86 1.82 1.85 1.89 1. 77 1.80 1.84 1.86 1,86 1. 81 1. 83 1. 87 1. 74 l. 75 1. 80 1. 85 1. 86 1. 86 1. 81 1. 90 *1. 70 l1. Y72 1. 74 1. 77 1. 80 1. 80 1. 76

However, the,V greater the amount of water in the cathode, other conditions being the same, the longer will 'be the life of the cell. The first co1- umn of mix wetness relates to the grams of electrolyte for each 0.4 gram of black. The pressure used was 30 lbs. per square inch, but such is not at all critical, it being desirable that the pressure used at the time of moisture impregnation should be at least about that intended for use upon the cell during its actual operation of delivering current. I

y In order to remove the mold ring, pressure applicator i6 and bibulous material I5 are preferably removed and a stripper plate I? is substituted, as shown in Figh, plate I'I being of the same size as the mix cake I2.' One purpose of the stripper plate is to hold the wet mix in place and' toprevent the material at the edges of the t mix from adhering to the inside of the mold ring mold rings may be provided sothat; as the cathodes are molded, astripperjpljate may be laid in place on each cathode andn permitted to. remain inr position until a sufficient A, number of cathodes havebeen rfnolrdedrto prpvidethe number of cells required Vvfor a battery of afpredetermined size.

With the st ripper plate andf mold ring in the position Shown Fgnaihe Cathodeiis not eX- posed to ainanla-r ere islittle opportunity for the mix to lose moisture; 4and when a battery-is to beasseinbled, thecathode which is-rst molded has` substantially, rticle same niclilstiirel content as the cathode las/t mold .thef'cells are ...uni-

' form. The Ystripper pla swma be of any weight up to Ythe meantime.primaextrusion of, the mix Ywhen the rnoldri u raised and the plates may contenenti-1U@ manipulated .by han# d ynor the blotting' paper med. t0 ihesize 0f g. 4, but saidjpaper Stripper plates ,arejpreferably used, how- A ever, and a sucient number off'theplates and ri.' ,and cette@ `the Ebner. *s

.Pile Pressure ap.-

piieator It is moved down into the momv ring II. Following the compression stroke the pres-H formation of air pockets between the mix Vcake and its support. Thus the cellophanev separator sheet I0 has the moist mix cake I2 formed on one side of it, While on the other side of it is the immobilized electrolyte layer I9 containing cotton netting to prevent the electrolyte material j from spreading laterally under pressure, as mentioned in thev prior patent of Cahoon et al., 2,612,538. With the zinc layer I8 and the electrolyte material I9 adjacent to the mix cake t2', the unit thus formed constitutes an assembly unit ready for embodiment in a dry cell of the type disclosed in said aforementioned Cahoon et al. Patent No. 2,612,538.

The particles of carbon for this wet mix cathode portion I2 are preferably of the nature of acetylene black, i. e. theyrare carbon blacks with chain type structure having a means ultimate particle hang from the lowpoint Voran unevenI surface of a saturated bib'ulous material.

The presentimention is an improvement in andthus it is difiicultto prepare a homogeneous wetcathode 4mix for application to .the anode assembly and to apply it to the anode assembly v 'in a uniform layer yfree from air pockets; but in diameter of from 5 to 10 millimicrons and Ahigh Y gas sorption, and they are relatively soft. Acetylene blacks as well as certain gas blacks have these characteristics. Y y

Among the advantages of this invention may be mentioned the provision of a homogeneous, uniformly moist wet mix containing no air pockets and providing good contact with the con tiguous portions of the cell. The amount of moisture -contained in the mix is readily controlled by the amount of moisture to be squeezed from the bibulous material I5. The amount of moisture in the cathode may be regulated by the pressure applied to the bibulous material and by its thickness and water absorptive characteristics. For any given pressure, the same amount of water may easily be supplied to all cells by using the same thickness of the saine bbulous material for each wetting and having lthe material saturated with the liquid. Greater or lesser amounts 4of liquid may be supplied by using thicker or thinner layers vofl bibulous material or using material having greater Aor lesser absorbing characteristics, but alwaysusing a saturated bibulous layer. Also, greater or lesser amounts of liquid may be supplied by using greater or lesser pressures. The least desired method of supplying liquid is by using bibulous layers which are less than saturated with the liquid as it is difcult to gauge the amount of liquid in the material where it is less than saturated. Where the bibulous material is used in an unsaturated condition it is preferred to obtain this condition in a standardized procedure, for instance, by adding liquid to standard pieces of material until each piece has the same weight or by saturating the pieces and then passing them between rollers or otherwise compressing under a standard pressure or to a standard weight. The kraft paper.

I4 serves also to spread the liquid over the surface of the black quite uniformly and prevents the liquid from contacting the black in the form of drops, for instance, such partial drops as may the. process of the present invention a homogeneous layer of dry or substantially dry black is quite easily prepared in the moldv and by wetA ting and compressing the black in situ a homogeneous wet cathode is easily, prepared Without danger of` air pockets lying next'to theA anode assembly.4` Furthermore, by usingl the 'present process. the wet cathode mix is eXDosed to air, for a minimum length of time, whereas in the` case where a batch of vwet mix is made and then used for the preparation of Vsuccessive cathodes.

l there is opportunity for the prepared but unused mix to dry materially betweenthe preparation of the firsty and last cathodes. Moreover, cathodes made according to the present invention can .be prepared with more water and yet hold their shape v(in case along life cell is desired) than can cathodesmade from previously prepared Wet mixes. n The phenomenonis believed to be due to the fact that where a mix of black and Water is stirred, too much water forms a weak water film on each particle which resists interlocking of the particles and -gives a structurally weak mass; but in thecase where water is gradually applied andv is applied. simultaneously with pressure, the particles are gradually interlocked and are supplied with gradually' increasing amounts of water up to the point where maxmumlinterlocking and strength are' obtained and any extra water distributes pverthe rfree surfaces ofthe particles without materially disturbing the previously formed bonds.

The present invention. has made possible the elimination of manufacturing, handling, and` storage diiiiculties heretofore encountered when moisture'is added to the mix cake by mechanically mixing the same therein.` As shown in the drawings, the mix ycake [2` is not of as large area as the cellophane I0, in order that'there may be a marginal portion of the cellophane free of mix to thereby' reduce the danger of the cell becoming short'circ'uited.'

In place of the bibulous sheet a substantially non-coinpressible layer of porous carbon or stone which does not react with electrolyte may be used on top of the kraft paper. A measured quantity of electrolyte solution is added to this wetting head, which `is attached to the press member and on compression the electrolyte solua tion penetrates the black by 'capillarity V.Such porous wetting head may be permanently attached to the pressure member of a molding machine and fed with electrolyte for transfer to the mix during compression but without compressing this porous wetting head..

What is claimed is:

1. .The processr of forming a dry cell having a thin wet mix cake of carbon black, which black is initially fluffy, which comprises spreading a layer of carbon black within a mold ring contiguous the edges of the black, placing on the layer of carbon black in the mold ring a layer 7 of' bibulous material which carries an amount'of liquid sufficient to effect a bonding of particles of the carbon black throughout the extent thereof, compressing the carbon black and layer of bibulous material substantially uniformly over the entire area of the layer of carbon black and wetting the carbon black with liquid pressed out of the bibulous material.

2. In a process of forming a thin, dry cell having a Wet mix cake of carbon black, the improvement for wetting the carbon black without causing it to ball up', said improvement including spreading a layer of carbon black which is initially uffy within a -mold ring contiguous the edges of the black, placing on the layer of carbon black Withinthe mold ring a distinct layer of porous material, said porous material being wetted with a liquid containing water and a stable wettingagent, and then applying pressure to said carbon black and porous material substantially uniformly to wet the carbon black with liquid from the layer of porous material.

3. The method of forming and wetting a mix cake portion of a thin cathode comprising placing a shallow molding ring on a'porous separator, filling dry carbon particles in said ring, levelling off the carbon by running a scraper blade over the top of said molding ring, rejecting the excess carbon material over the Vedge of said ring, placing a thin 1raft paper over the layer of carbon particles in the mold, pressing a wet porous material against the kraft paper, forcing moisture from the wet material and passing the same through the kraft paper into said mix within the molding ring.

4. The process of forming a thin dry cell having a wet mix Ycake of carbon black, which black is initially uffy. which comprises spreading a thin layer of carbonV black within a mold, placing a distinct layer of Wet porous material on the carbon black, compressing the layer of carbon black with said layer of porous material disposed in liquid and pressure transfer relation with at least one surface of the layer of carbon black, said' porous layer carrying Ian amount of liquid sufficient to effect a bonding of particles of the carbon black throughout the extent'thereof after they have been compressed, and maintaining the pressure of the porous material on the carbon black until the black is wetted throughout its extent by capillarylaction from the wet porous material. I

5. A process according to claim 4 in which the liquid with which the carbon black is wetted is 8 2 an electrolyte solution and the amount of Ythe liquid passed into the'carbon black is between 1.65 g.and 2.90 g. per .4 g. of dry carbon black.

6. A method of forming a thin compressed Wet mix cake of substantially uniform porosity from finely divided carbon black which comprises forming a layer of the' carbon black in a mold, placing on said layer of carbon black a distinct layer of a wet porous mass outside the carbon' black which porousmass carries an amount of liquid greater in weight than the weight of the layerA of carbon black, applying pressure to said layers whereby liquid is expressed from the porous mass and is distributed substantially uniformly from an adjacent surface of the porous material and into the layer of carbon black.A Y', 1-

7. A process according to claim 6 in which the particles of said materialr have ajdia'meter ape f Yproxiinately between 5 andv100 millimicrons, the' vpressure applied is sufficient to lcompress said layer to less than half its former depth, and the amount of moisture is sufficient to form the cakey With about 15% to 20% porosity therein. y

8. A process according to claim 6 in which said vuniform distribution of moisture is obtained by, K the application of pressure to a substantially satg Y urated layer of bibulous material.V

9. The process of forming a cake of carbon black which comprises substantially simultaneously compressing said'carbon black and extruding moisture from a layer of bibulous material between the cake and an objectto which the stress forV compression is applied, and reducing the danger of carbon black adhering to the bibulous material by an absorbentsheet of material between the cake and bibulous material, said absorbent sheet having a smoother and less adherent surface than does the bibulous material,

whereby the danger ofthe c-arbon black adher- Y ing to the bibulous material is reduced.

HERMAN MEREDITHV ZIMMERMAN.

References cited in thegfiie of this patent UNITED STATES PATEN-'rs Whaley Jan. 4, 1949 

1. THE PROCESS OF FORMING A DRY CELL HAVING A THIN WET MIX CAKE OF CARBON BLACK, WHICH BLACK IS INITIALLY FLUFFY, WHICH COMPRISES SPREADING A LAYER OF CARBON BLACK WITHIN A MOLD RING CONTIGUOUS THE EDGES OF THE BLACK, PLACING ON THE LAYER OF CARBON BLACK IN THE MOLD RING A LAYER OF BIBULOUS MATERIAL WHICH CARRIES AN AMOUNT OF LIQUID SUFFICIENT TO EFFECT A BONDING OF PARTICLES OF THE CARBON BLACK THROUGHTOUT THE EXTENT THEREOF, COMPRESSING THE CARBON BLACK AND LAYER OF BIBULOUS MATERIAL SUBSTANTIALLY UNIFORMED OVER THE ENTIRE AREA OF THE LAYER OF CARBON BLACK AND WETTING THE CARBON BLACK WITH LIQUID PRESSED OUT OF THE BIBULOUS MATERIAL. 